The invention relates to metal halide and mercury arc lamps and to the thermal control of a metal halide or mercury arc lamp and associated fan in operation through the use of a directed air flow.
The invention in general relates to the thermal control of an arc lamp in operation and more specifically to the use of a directed air flow to the arc chamber of the lamp.
In the prior art it is common to use arc lamps with a reflector to form an assembly which are used in an enclosed housing or a sealed light module to provide directed light which is used for projector systems and the like. When used in an enclosed housing or sealed module, an arc lamp generates high internal heat which can result in short lamp life and high lamp infant mortality rate due to the localized heat generated by the lamp in combination with a reflector within the confines of the housing or module. In these instances, venting and laminar flow cooling techniques are often employed to lower thermal values such that system installation is possible. Yet, in systems of this type it is common that highly loaded arc lamps exhibit a short life of 200 hours and a high infant mortality rate of less than 100 hours with an average life of approximately 400 hours or 20-45% of rated life. Lamp life times of this duration are unacceptable and result in high replacement cost to the ultimate user and discourage their use in systems of the type described above.
In addressing the problems described above, the prior art has believed and been taught away from directing any coolant air flow directly onto the lamp chamber in that such an approach would be unsatisfactory, and result in instability of lumen output and color. There has therefore been a continuing need in the field for a system which would allow for extended lamp life without compromising stability of lumen output or color for arc lamps used in the systems described above.
It is therefore an object of the present invention to provide a method of lamp thermal control which overcomes the problems of the prior art described above.
It is another object of the present invention to provide a method for thermal control which increases the life of a sealed light module which includes an arc lamp, reflector and fan.
It is a further object of the present invention to provide for a method of lamp and fan thermal control which results in improved lamp and fan life.
It is another object of the present invention to provide a method for increasing lamp life without compromising stability.
It is yet another object of the present invention to provide a method of thermal control in which the arc lamp achieves thermal equilibrium in a relatively short time.
It is a further object of the present invention to provide a method for the thermal control of an arc lamp through the directed air flow to the interior at the lamp chamber and surrounding reflector.
It is a further object of the present invention to provide a method of increasing the life of an arc lamp assembly.
It is yet a further object of the present invention to provide for lamp and fan thermal control for an arc lamp positioned in an enclosed chamber which utilizes controlled direct air flow directly around and past the lamp chamber.
The invention is directed to situations where a lamp assembly, which includes an arc lamp and a reflector, is used in an enclosed housing or as a sealed module which acts as a high intensity light source. In the present invention, an ambient air flow is allowed to flow into the interior volume of a sealed light module defined by the reflector geometry, and pass over the lamp chamber at a critical angle from the vertical. Lamp thermal control is effected, resulting in a dramatic increase in lamp life and a reduction in infant mortality of the lamp. The process of the present invention overcomes the problems of the prior art in systems of this type, in that lamp failure caused by the early onset of devitrification of the lamp chamber and quartz to foil hermetic seal separation are eliminated. Through the use of this process the anode temperature dropped approximately 50-70xc2x0 C., and the cathode temperature dropped approximately 30-40xc2x0 C. By employing this invention lamp life is improved by a factor of 3.
The system described above includes a fan which facilitates the air flow and is usually positioned to operate in the exhaust mode. Because the air flow passing over the fan has been heated by being passed over the hot lamp, the heated air passing over the fan has been found to significantly reduce fan life and result in early failure of the system. In order to overcome early fan failure due to thermal stress, it has been discovered that the placement of a vent or opening, i.e. waste gate, formed adjacent to fan functions to lower the air flow temperature resulting in less thermal stress on the fan. More specifically, the waste gate functions to introduce additional ambient air at a lower temperature to heated air flow from the lamp which overall reduces the air flow temperature passing over the fan thereby increasing the life of the fan and light module.